The invention described herein relates to a vermiculite composition having enhanced chemical exfoliation and ability to provide a high yield of single platelet material and to products formed therewith. Specifically, the present vermiculite composition is composed of particulate vermiculite mineral species having a density of 2.3 g/cm.sup.3 to 2.7 g/cm.sup.3 which has cations of lithium or organo ammonium intercalated between the mineral's platelet layers.
Vermiculite ore is composed of micaceous minerals, chemically identified as a hydrated magnesium-aluminum-iron silicates and characterized by a platelet structure which exfoliate or expand in a single direction when subjected to high temperatures or chemical treatments. The minerals occur naturally in an unexpanded state, and are mined in conventional manner.
The term vermiculite refers to mineral species characterized by a layer latticed structure in which the silicate layer units have a thickness of approximately 10 A. The main elements present in the layer are magnesium, aluminum, silica and oxygen with the layers being separated by spacing of approximately 4.ANG. which is occupied by sheets of water molecules associated predominantly with cations of as magnesium and calcium. The layers have considerable lateral extent relative to the thickness of the 10 .ANG. platelet layer. The vermiculite minerals include minerals composed wholly or largely of vermiculite minerals or minerals of a mixed layer type containing vermiculite platelet layers as an important constituent, such as hydrobiotite, and chlorite-vermiculite.
The vermiculite ore, as mined, is associated with other minerals and undesirables. The crude vermiculite ore normally contains about 15 to 30 weight percent commercially desired vermiculite. This crude ore is beneficiated by various known surface chemistry techniques to separate the gangue from the expandable material. For example, the crude ore is normally washed with water to remove clays and other associated fines. The remaining material is subjected to screening (with optional prior crushing to reduce particle size) to separate sand, rock and other debris from the platelet materials which contain non-expandable minerals (mica, etc.) and expandable materials. These are separated by treating the material with a surfactant and subjecting it to flotation or wet concentrating table techniques to recover vermiculite ore concentrate. Conventional ore concentrate is generally composed of 85 to 99 weight percent expandable vermiculite minerals ore having a range of specific densities ranging from less than 1.9 g/cm.sup.3 to over 3.0 g/cm.sup.3, depending on its platelet configuration.
Vermiculite minerals are well known for their capacity to undergo expansion to several times original volume. The process of expanding vermiculite ore concentrate by heating is referred to as thermal exfoliation. This process is conventionally achieved by a continuous procedure in which vermiculite concentrate are fed into an expansion kiln or oven, heated rapidly to temperatures in the range of 1100.degree. F. to 1900.degree. F. and the resultant expanded vermiculite product removed from the heating zone as additional unexpanded material is introduced. Thermally exfoliated vermiculite is conventionally used as packing, thermal insulation, filler material and the like.
Vermiculite ore concentrate has also been caused to expand by osmotic swelling. The ore concentrate is initially subjected to an aqueous electrolytic solution, such as aqueous sodium chloride, and then immersed in water to cause swelling by osmotic pressure. U.S. Pat. No. 3,062,753 to Hayes utilizes a combination of osmotic swelling followed by thermal treatment to cause improved volume yield of vermiculite ore concentrate.
In recent time, the use of asbestos as a material which enhances thermal properties of materials has been found unsuitable because of health reasons. With the withdrawal of asbestos from use, the need has arisen for new materials to enhance the thermal and fire resistance of many products. High performance organic and inorganic materials, such as polyimides, aramides, graphite and ceramic substances have been developed to fill the void. In addition, vermiculite dispersions composed of delaminated vermiculite resulting from delamination of the mineral species, have provided the needed enhancement properties. Although conventional ore concentrate and thermally exfoliated material have limited applicability as a coating or filler material for this purpose, vermiculite dispersions can be readily formed into sheets or applied to woven and non-woven materials and other substrates to provide the desired properties.
U.S. Pat. No. 3,325,340 to Walker describes the production of dispersions of delaminated vermiculite and the production of films and coatings therefrom. The patent discloses that dispersions can be prepared by treating vermiculite minerals with a solution containing a cation which can diffuse between the interlayers of the mineral's structure and cause gross swelling in the direction normal to the main cleavage plane of the layer during immersion in water, immersing the treated vermiculite in water and permitting the swelling to occur, and shearing the swollen vermiculite to delaminate the layers and form a suspension of vermiculite flakes or platelets.
U.S. Pat. No. 3,325,340 discloses agents which can be used to promote the swelling of the vermiculite to be the chloride salts of the following cations: n-butylammonium; iso-amylammonium; isobutylammonium, n-propylammonium and the like; the cationic form of amino acids, such as lysine or ornithine, and the lithium cation. The focus of this patent is the ability of the disclosed cations to promote vermiculite swelling and delamination. The predominant material used are n-butylammonium chloride and lithium chloride salts. U.S. Pat. No. 4,812,260 to Nelson further used other organic ammonium salts, such as those of allylammonium, to promote swelling. The dispersions formed according to the processes of Walker and Nelson tended to be unstable, in that the vermiculite platelets tended to reaggregate and to settle out over a period of time. However, when the platelet dispersion contained certain anionic chelating agents, as taught in U.S. Pat. Nos. 4,655,842 and 5,102,464, the resultant suspension was found to be more stable.
One of the major drawbacks of the dispersions formed according to known processes is their lack of uniformity and the presence of platelet material which has not delaminated to a high degree. The vermiculite ore concentrate does not have a sufficiently high degree of delamination into single (or few) layer platelet material to substantially eliminate high multiple platelet material. This may be due to the incomplete swelling of the vermiculite mineral species and/or due to the lack of uniformity of the vermiculite ore used. The resultant dispersion, thus, contains agglomerated material which hinders the production of suitable treated or formed end product. For example, the coatings and sheets formed from the dispersions tend to be non-uniform.
It is an object of the present invention to provide a vermiculite composition which has enhanced osmotic swelling and delamination capabilities.
It is further object of the present invention to provide a process for forming substantially uniform vermiculite dispersions having a very high degree of single platelet material.
It is a further object of the present invention to provide sheet materials and coated materials using the present improved vermiculite dispersions.